Taking into account that the geometrical dimensions should be constant in time, voltage output of the magnetic coil can be expressed by This presents the relation between current, coil area and its distance from wire the current is observed on. A magnetic coil equivalent circuit can be described in the simplest way with a capacitor, inductor and a resistor (see fig. As it turns out from the electric field theory applications, there is a quite good relation between coil electrical characteristics and its dimensions. In order to assess the magnetic flux acquired by the coil, the magnetic flux should be integrated to make up the area of the Frameįor the first criterion, one should establish a relation between the bandwidth of the coil and its physical build. B is magnetic flux density created by the current passing through the wire. Application of magnetic loop for measurement of current along a wire. 2) Coil had to provide as high output as possible for the high-frequency signals.įigure 1. 117ġ) Coil system had to have wide bandwidth to detect the signals with smallest durations and highest frequencies. Where l – distance from wire a – frame length µ0 – magnetic constant 4*10-7 H/m. In case of DC, magnetic field density near the wire can be calculated as This is followed by a small step, in order to measure current in a wire the magnetic sensor should be placed in the vicinity of the wire to be measured (see fig. As The magnetic field lines are located perpendicular to the wire, the maximum flux linkage (i.e coil could hold maximum numbers of magnetic field lines) can be achieved when sensing coil is also perpendicular to the wire. Most important in our application would be the rate of current change of the observed application.Īpplication of current measurement Every wire, which has some current passing through it, has also a magnetic field around it. Higher relative magnetic permeability leads to greater output. Φ = B⋅ A where B – magnetic flux density A – magnetic sensor coil area.įirst of all, the larger the area of the coil, the larger the output. Magnetic flux is determined by magnetic flux density and the coil area Ψ = w⋅Φ where w – number of turns in sensor coil Φ – magnetic flux. Flux linkage is determined the coil flux and number of turns in the coil This means that the electromotive force depends on the rate of change of the flux linkage acquired by the coil loop area. Where e – electromotive force Ψ – flux linkage t – time. Operating principle is based on the Faraday’s law dψ e=− To make a magnetic coil sensor, one would need to make a coil consisting of N turns of wire. This formula in essence holds all the factors that make up the magnetic sensor coil sensitivity.ĭue to its simplest construction and trivial operating principles magnetic field sensor coil has been known and used for over a hundred years.
Keywords Magnetic field sensor, fast transients, partial discharge measurement.
Taking into account the above, magnetic sensor coil output can be written as e ≅ − Awµ As the mechanism of the magnetic field source is not determined, the more precise magnetic field strength formula will not be established. Obviously, strength of magnetic field is relative to actual current value H ≅I Magnetic flux density is related to magnetic field strength B = µ⋅H where µ – relative magnetic permeability H – magnetic field strength. However, it turns out that in this case one would need to take into use a much more complicated model of the current sensor coil. This said, it is reasonable to assume its characteristics are prefect for measurements of current travelling waves on the power lines, for the application of fault locating. Furthermore, it provides the possibility to measure high-frequency currents from a distance, in a non-intrusive way. Some researchers have established that it would be one of the most perfect sensors available, as it provides excellent sensitivity, bandwidth, lowest noise etc. Magnetic field sensor coil in fast transient measurement application Lauri Kütt, Jaan Järvik Tallinn University of Technology, Ībstract Induction coil sensor is basically the simplest magnetic field senor. 10th International Symposium „Topical Problems in the Field of Electrical and Power Engineering“ Pärnu, Estonia, January 10-15, 2011
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